We have reported that intracerebroventricular administration of oxytocin to virgin female rats induces a high incidence of rapid-onset full maternal behavior. The incidence of maternal behavior is dose related. Extensive specificity studies have shown that, in addition to oxytocin, arginine vasopressin and tocinoic acid (the ring structure of oxytocin) induce a lesser, though statistically significant, rate of full maternal behavior. Prostaglandin F2alpha induces transient partial maternal behavior. Many substances are inactive. The rapid induction of maternal behavior, full or partial, by active substances appears to be estrogen dependent. Thus our work is addressed to the triggers of maternal behavior as contrasted to the endocrine permission of such behavior. Our work, centered on peptides, complements earlier elegant descriptions of the role of steriod hormones. We propose to investigate the importance of brain release of endogenous oxytocin and arginine vasopressin th the onset of maternal behavior in parturient rats and to the maintenance of maternal behavior in nursing rats. We will assess the impact on onset and maintenance of maternal behavior of manipulations that deplete extra hypothalamic brain sites of oxytocin and vasopressin (lesioning of the paraventricular nucleus and/or the suprachiasmatic nucleus). For the same dependent variables we will assess the impact of manipulations that prevent oxytocin and vasopressin from interacting with receptors (intracerebroventricular injection of oxytocin- and vasopressin-directed antisera or infusion of competitive inhibitor analogs of these peptides). We propose to measure regional brain content and CSF and blood levels of oxytocin and arginine vasopressin and brain uptake of [3H] oxytocin in female rats in hormonal states either conducive or inimical to the onset of maternal behavior and in nursing and post nursing rats that have given birth. We intend to determing the loci at which oxytocin and arginine vasopressin have their maternal behavioral effects by injecting these peptides into selected brain sites.